In industrial vehicles known as skidders have been in use for many years serving the function of pulling felled trees from a logging site to a landing where they can be conveyed to a facility for processing the wood. Skidders originally involved vehicles having a chain connected to the log to drag it out of the logging site but have evolved to skidders where they have grapple hooks to physically hold the felled timber to carry it out. Skidders have been developed to enhance operator efficiency, safety and productivity in spite of the arduous duty cycles demanded of skidders.
One of the problems with skidders is that they must operate over a highly irregular terrain, caused mainly by the stumps of logs or trees that have already been felled. The terrain created by the tree stumps is so severe that it becomes extremely difficult for the operator of a skidder to navigate it over the tree stumps to the landing where logs would be carried away in volume. Current skidders use manual transmissions with clutches and other mechanisms so that the operator, in addition to compensating for severe inputs to the steering mechanism, must shift gears to provide a practical speed through the field to the landing where the logs are delivered. This activity requires that the operator free a hand to shift the gear mechanism thus leaving only one hand on the steering mechanism. The problem of maintaining a proper speed is exacerbated by the fact that the operator is jostled so that the only way to maintain any sort of control is to depress the power lever or throttle to the floor so that the operator can be held in place in the operator seat in the cab.
Another problem with skidders is that the prime mover, or internal combustion engine, used to power the skidder also drives a hydraulic pump that powers various actuators employed to, among other tasks, grapple the log to be transported. It is essential that the engine RPM be high enough to provide sufficiently quick actuator response time to ease the burden on the operator while keeping the ground speed at an appropriate level in light of the terrain.
What is needed therefore is a propulsion system that reduces the adverse requirements on the operator of such skidder vehicles.